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Discussion Starter #1
I have dual Battery in the trunk i just want to know before drilling holes, by your experience the best grounding spot.

am running now two positive 1/0 gauge cables from front battery to trunk i tried to ground the rear battery to the trunk lifters but it's not good spot anyone have any picture for the best ground spot i have to drill and am afraid of my fuel tank.

Best regards
 

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On the passenger side of the trunk, lift up the mat and look or feel for a knock out. It will allow you access to the frame where you can ground right to it. That is what I did when I moved my battery to the trunk.
 

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Discussion Starter #3
On the passenger side of the trunk, lift up the mat and look or feel for a knock out. It will allow you access to the frame where you can ground right to it. That is what I did when I moved my battery to the trunk.
Thanks for you reply
you mean there is a place there i can ground it without run it underneath my car?

I will search for it anyway
 

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The factory runs all the grounds to the sheetmetal of the vehicle body, not the frame. The factory runs a primary ground for the fuel pump and rear lights to a self-tapping screw on the driver's side trunk hinge support.

For a trunk mounted battery, I would drill a 3/8" hole in the trunk hinge support closest to the battery or the to metal of the rear deck, and put a 3/8" bolt with an serrated star washer (with BOTH internal & external teeth) as ground points for the negative cable.
 

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The stock battery had a ground to the frame and the fender. While it is a very good idea to ground to the trunk hinge, there is absolutely nothing wrong with a ground to the frame for a battery in the trunk---------but as Brick B-body says also use the hinge
 

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Stock GM Negative Cable

The OE GM negative battery cable has two leads. Take a look at the parts schematic attached below.

The Negative cable is #10

1.) Body Ground, skinny wire. About 1 foot in length from the negative battery terminal to the fender secured with a self-tapping hex screw (#9) and dual (inside & outside) serrated star washer (#8).

2.) Engine Ground, fat cable. Runs from the negative terminal under the coolant tank, then makes a turn to the alternator and grounds the engine block with a nut (#12)

With factory wiring, nothing is directly grounded to the frame, nor is the frame directly grounded to the battery. The closest to the frame being grounded is by the body mount bolts.

Nothing wrong with running ground wires to the frame, but a cable MUST also be run from the battery negative terminal to the frame to make it electrically sound. Gary does exactly this with his LT1 H/O Caprice / Impala SS / Roadmaster cables, shown here, at the bottom of the page. Notice the third negative lead (middle length) specifically for the frame: http://innovativewiring.com/?page_id=175
 

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I have Garys cables and they are the best. They ground to the frame as well as the body in the engine bay and the trunk area. When ever changing or adapting the electrical system in a car, adding a ground to the frame is highly suggested. But keep all grounds to the sheet metal, just add the frame ground.
 

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Do you have 1 battery in the stock location and 1 in the trunk, or 2 in the trunk?

Ground the battery to both the frame and the body in the trunk. Also ground the engine to the frame. The frame grounds need to be at least as large as the positive lead to the starter.
 

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Discussion Starter #9
Thanks for reply

i have optima battery in the front reading 14.7v without extra batteries when i connect my Acid battery in the rear voltage drops to 14.5~14.4v is it normal?

See the attached picture this is my rear ground.
 

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Do the big 3/4 upgrade up front and in the rear i use the rear seatbelt bolt under the seat for ground. Works great. I have 1 run of 1/0 gauge from my front battery to rear battery and only have .1v difference. Clean off the area under there real good. I used a dremel to grind off any paint too
 

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One thing to think about is how the battery up front is grounded. There is a frame ground and a fender ground. From everything I've read as well as inspecting my own vehicle, I haven't seen anything that supports a good electrical connection between the body and the fender. I added a small piece of 1/0 wiring behind the small support that runs between the firewall and the fender. That'll ensure that anything you ground to the body of the vehicle, almost anywhere you ground it, has a good return path for the current that it normally wouldn't have had. And for those people who mentioned Gary's wiring, I'll vouch for his HO wiring. I've had it on my car for a few years now and love it. It looks clean and factory but offers the performance I need with my 200 amp alternator.
 

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Easy Trunk Grounds

The factory grounds in the trunk are simply secured to the hinge support with a self-tapping bolt, not the strongest way to do it. Looking nearby to the trunk hinge boxes, I found existing holes about 1/4" and 3/8" in size, that can be used to create much better grounds. These holes are present in trunk hinge boxes on both sides and need no drilling to use.

I'm a fan of using a bolt, serrated washers (internal & external teeth are best) and a flange nut, to really crank down on the ring terminal to body ground connection. I cut off the factory ground terminals and crimped on 1/4" ring terminals with more surface area. These upgraded terminals were then moved from the self-tapping bolt, to a 1/4" bolt higher up the hinge support.

The 3/8" holes were used in the same way to ground my amps.
 

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Did you grind or sand away the paint that's under the heads of your fasteners? Doesn't look like you did based on the photos. That must be done or you will not have an adequate ground path.
 

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Did you grind or sand away the paint that's under the heads of your fasteners? Doesn't look like you did based on the photos. That must be done or you will not have an adequate ground path.
The factory uses external serrated star washers on the fender ground by the battery, and internally serrated ring terminals on many ground wires. None of these factory grounding points have any paint removed.

The use of grounding washers with both internal & external teeth does not require any paint scraping. When tightened down, the teeth cut past the paint and any oxidation. The teeth dig into both the ring terminal and body sheetmetal creating metal-on-metal contact without excessive paint removal. Pronouned teeth gouge marks can be seen upon disassembly on both surfaces.

Using the Bolt/Serrated Washers/Nut setup allows you to crank down the connection as tight as you want to fully engage teeth into the metal surfaces without fear of stripping like the factory self-tapping bolts. There is more than enough clearance around the holes in the trunk hinge box to fit a tightening wrench or rachet and a backup wrench.

For both making new grounds, and upgrading existing ones, I bought an assortment of grounding washers with both internal & external teeth like below.
 

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The factory uses external serrated star washers on the fender ground by the battery, and internally serrated ring terminals on many ground wires. None of these factory grounding points have any paint removed...
The factory grounds are also designed to carry far less amperage than that which is carried by a 2 gauge (or heavier) wire used in a stereo system.
 
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